The manufacture and assembly of ornamental and security iron picket fences has been gradually improved upon in the prior art, resulting in fences which are cheaper to manufacture and easier to install.
Van Dorn, U.S. Pat. No. 189,543, discloses a picket fence assembly in which pickets have a notch on at least one side thereof, the notch providing a shoulder which engages with the edge of a horizontal rail when the pickets are inserted into holes in the rails. The holes in the rails correspond to the shape and size of the picket in cross section and the shoulders of the pickets engage the rails when the pickets are rotated one-quarter turn. In one embodiment a collar slides over the picket and wedges between the picket and the rail on all sides of the picket, thereby further securing the picket in place. A rigid overall structure is created. End support posts attach to the rails with a grooved wedge and secure the fence against vertical and longitudinal displacement. Vertical and lateral adjustments are made by adjusting the wedge connections between rails and posts and rails and pickets respectively.
Wedges must be placed in each rail-picket joint to prevent rotation and loosening of the pickets. Wedges may become loosened over time and with exposure to the elements, and may require replacement, resulting in increased expense.
Hebda, U.S. Pat. No. 4,883,256, discloses a picket fence and method of construction. The pickets are noncircular, and are inserted through corresponding holes in upper and lower rails. The holes are of the same shape and size as the cross sections of the pickets. The pickets are notched at the level of the upper rail and at the level of the lower rail at each corner so as to enable engagement of the pickets with both of the rails, which prevents vertical displacement of the pickets. The pickets have transverse through-holes which are aligned and receive a rigid transverse rod, thereby preventing rotation and vertical and lateral displacement of the pickets. The rod serves to stabilize the structure and to render the fence less susceptible to surreptitious disassembly, thereby increasing the security function of the fence.
Use of a rod to lock the picket into place adds manufacturing costs in terms of the cost of the rods and the costs of adapting the pickets to receive the rod, and increased labour cost due to the requirement that the pickets must be accurately aligned in order to pass the rod through them. Difficulty with alignment and insertion of the transverse rod would be anticipated in the case of hilly terrain or irregularly constituted terrain.
The present invention improves upon the prior art by preserving the functional advantages set out in the prior art, such as vertical and lateral stability and protection against surreptitious disassembly, while reducing both manufacturing and assembly costs and simplifying the assembly process. The present invention provides an improved structure which prevents further movement of pickets subsequent to initial rotation from an "assembly position" into a "locking position". Furthermore, the present invention may be assembled with ease on any type of terrain.